I am getting no where getting the corner castings to budge even the smallest amount. There are no side rails on the boat since they both have been cut and removed, so only the 2 castings are connected in the forward and aft by a cross bar. I have tried hammering with a rubber mallet, soaking with liquid wrench and heating with a propane torch. I guess I need to kick it up a notch.....

Do I need to worry that if I start pounding very hard on the casting, that I will break loose the tube that goes into the hull? Has this ever happen to anyone?

Has anyone ever cut a vertical slit in the casting to pry it open? The one I really want off is already cracked on top so I don't care if I destroy it (it's in the back).

I have only see rivets used to attache to the crossbars and only a the large bolt is used to secure the castings to the pylons of the pontoons.

I just removed my whole trampoline structure to start my restoration, and the only why they were coming off were with a lot of persuasion with a rubber mallet. Do Not use a steel hammer unless you want to break the castings, but you can beat on it pretty much as hard as you can with the awkward upswing with a rubber mallet.

The rivets that I asked about are connected to the cross bar. I asked about removing them to help eliminate any side to side pressure that might be keeping the casting from coming straight off the tube. I did remove the large bolt that holds the casting to the tubes.

I am trying to remove the castings from the pylons. I have removed the bolt and used a mallet but it's not coming off. My question is how hard can I hit the casting without damaging the connection between the hull and the pylon. I don't want to pull the pylons out of the hull!

The pylon is fiberglassed in there pretty well. As said I just did this the other day and I was hitting it pretty hard. This isn't something your just going to be tapping off. Mind you I was a Derp at first and forgot to loosen my tramp so the first two require a lot more pounding, but it sounds like you don't have a tramp on right now.